CVE-2025-30355: synapse Input Validation Flaw — Fix

Description

Synapse is an open source Matrix homeserver implementation. A malicious server can craft events which, when received, prevent Synapse version up to 1.127.0 from federating with other servers. The vulnerability has been exploited in the wild and has been fixed in Synapse v1.127.1. No known workarounds are available.

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CVSS v3.1 Score

7.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H

Weakness Type (CWE)

CWE-20 Improper Input Validation

Affected Products

Vendor	Product	Versions
matrix	synapse	< 1.127.1

References

Advisories & Patches

https://github.com/element-hq/synapse/commit/2277df2a1eb685f85040ef98fa21d41aa4cdd389 https://github.com/element-hq/synapse/security/advisories/GHSA-v56r-hwv5-mxg6

Other References

https://github.com/element-hq/synapse/releases/tag/v1.127.1

Frequently Asked Questions

What is CVE-2025-30355? +

Synapse is an open source Matrix homeserver implementation. A malicious server can craft events which, when received, prevent Synapse version up to 1.127.0 from federating with other servers. The vulnerability has been exploited in the wild and has been fixed in Synapse v1.127.1. No known workarounds are available. It has a CVSS v3.1 base score of 7.1 (HIGH).

How severe is CVE-2025-30355? +

CVE-2025-30355 has a CVSS v3.1 score of 7.1 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2025-30355? +

CVE-2025-30355 affects products from matrix, specifically: synapse. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-30355? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2025-30355